Techniques of human body communication in which communication data is transmitted and received through living bodies such as human bodies have been developed in various fields. For human body communication, a communication apparatus using a human body as a part of the transmission path is provided with two electrodes. One of the two electrodes is a signal electrode connected to a signal line whereas the other is a reference potential electrode connected to a ground potential, having a reference potential, of the communication apparatus. Signal electrodes are coupled to each other mainly through human bodies, whereas reference potential electrodes are coupled to each other mainly through a space and/or the earth ground. With these couplings, the communication apparatus transfers a difference in potential between the signal electrode and the reference potential electrode to the correspondent communication apparatus.
The coupling between the reference potential electrodes through the space and/or the earth ground is affected by the noise from other systems, or a fluctuation in potential of a signal on the human-body surface caused by an unintended coupling to a nearby human body. Accordingly, the reference potential becomes unstable, and the communication quality is impaired.